Current through electronic device

Dynamics of electronic carriers J = nev d = ne 2 F  /m* J =  F (lei de Ohm)  = ne 2  /m* = ne  v d =  F  = e  /m*  = e(ne  e + np  p )

NON-LINEAR EFFECTS ON THE MOBILITY Space-charge limited current J  (9/8)  V 2 /l 3 ********************************************** Poole-Frenkel effect J = ne  (E)E with

Capacitor – Electric Field

Dielectrics - Polarization

Dipole Moment  = 2a

DEVICE 3: OTFTs Organic Thin-Film Transistors DEVICE 2: OLEDs Organic Light-Emitting Diodes DEVICE 1: OPVs Organic Photovoltaics

DEVICE 1: OPV Organic Photovoltaics

Generations of Solar Cells First: PV p-n junction diode of crystalline silicon (market) Second: PV thin films of non-monocrystalline semiconductors (amorphous silicon, poly-crystalline silicon, cadmium telluride films, copper indium selenide/sulfide,...) (market) Third: Organic photovoltaic cells, photoelectrochemical cells, dye-sensitized Solar cells,...) (research) Fourth: Biomolecular cells (prevision) - Mimicking the nature.

MARKET

Sun: Total power Organic material Absorption

Equivalent circuit and characteristic curve I sc..... Short-circuit current V oc.... Open-circuit voltage I mp.... Current at maximum power V mp.... Voltage at maximum power Fill Factor FF = (V mp x I mp )/(V oc x I sc ) Current source Diode R c (contact + bulk) resistances R s shunt resistance

EFFICIENCY

Efficiency Quantum efficiency: ratio of the number of collected charge carriers to the number of incident photons (EQE or IPCE). Power Conversion Energy (PCE):ratio between the solar power produced by the cell by the power of the incidente flux of light

First generation: pn JUNCTION

Thickness  100  m

Second generation: Inorganic Heterojunction Thickness  5  m

Third generation: Organics

ELECTRONIC DEFECTS Poly(p-phenylene) - PPP Charge spin exciton singlet 0 0 Negative polaron - e 1/2 Positive polaron e 1/2 Negative bipolaron - 2e 0 Positive bipolaron 2e 0

In organic semiconductor the generation of carriers is a secondary process. Excitons (bound electron-hole pairs) are created by absorption of light, and should be dissociated, and then the carriers collected by electrodes) HETEROJUNCTION Thickness < 100 nm

2.5 % Efficient Organic Plastic Solar Cells S. E. Shaheen et al, Appl. Phys. Lett 78, 841 (2001) First High Efficiency

Dispersed electronegative species

Poly(disilanyleneoligothienylene) + C 60

Onsager effect T = 300 K  = 3 r  20 nm An electric field of the order of 10 5 V/cm already stimulates the dissociation mechanism

High Efficiency Cell (4.2 %) 4.2 % Efficient Organic PV Cells Wtih Low Series Resistances J. Xue et al, Appl. Phys. Lett. 84, 3013 (2004) Double heterostructure 20 nm donor-like layer-CuPc 40 nm acceptor-like layer-C nm exciton-blocking layer of bathocuproine (BCP)

High efficiency cell (4.6 %) Poly(ethylenedioxythiophene):polystyrenesulfonate Poly(3-hexylthiophene-2,5-diyl):[6,6]-phenil-C61-butyric acid methyl ester Copper phthalocyanine:fullerene High efficient organic tandem solar cells using na improved connecting architecture A.G. F. Janseen et al, Appl. Phys. Lett. 91, (2007)

Donor-acceptor mixture

Important characteristics Characteristics of OPV: High absorption coefficient (10 -5 cm -1 ) Short penetration depth Thin films (10 – 1000 nm) Important limitation for organic PV is the short diffusion length of the exciton

To mention Electrochemical Solar Cell

Summary

OPV End

DEVICE 2: OLEDs Organic Ligth-Emittng Diodes

Polymers and Small Molecules PLEDs and SMOLEDs

Most important luminescent polymers Poly(p-phenylene vinylene) Polyfluorene

Most important luminescent small molecules ALq3 Pentacene derivatives

Most important electrical and optical characteristics

IV curves ITO/PPV/Al ITO/MH-PPV/Al

Current vs Luminescence

JABLONSKI DIAGRAM

Absorption and Emission (molecules) Frank-Condon Efeect

Absorption and Emission of PPV

Photo and Electroluminescent emission

Detecteur 0º0º 180º 90º Analisateur P 1 (//) S-Film P1()P1() Laser Optical system to detect polarized photoluminescence

Disordered PPV Film Stretched PPV Film

Stretched PPV

Electronic Model and Distribution of conjugation lenght PPV

TECHNOLOGY

PLEDs – Blue and White

Ink Jet Printing Process Ink-Jet Printer Heads PLEDs are solution processable, and can be applied using ink jet printing processes

Printers

Technological Advances of OLEDs

Future? No, present!

Comparison OLED-LCD Light Diffuser Prism Sheet Polarizer Film Common Electrode Protective Film Glass Substrate Waveguide Plate Back Light Reflector Polarizer Film Black Matrix Color Filter Capacitor Alignment Film Liquid Crystal Spacer Sealant 7mm Typical TFT-LCD Potentially, up to 50% of the display cost is eliminated P-OLED devices can reduce costs significantly: No backlight unit No liquid crystal light valve No color filter Simpler bill of materials Simpler production method Display Electrode Glass Substrate 2mm Typical Cathode Anode (ITO) Glass Substrate P-OLED Glass Substrate Polarizer Film Emissive Layer Interlayer Hole Conducting Polymer 200nm

White OLED (Organic Lighting)